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Discussion Starter · #1 ·
Came across something the other night shooting that I can't explain... I've been playing with different tip weights (100 vs. 125 grain) on the same shafts (GT Hunter "something or other", all the same length and all in the batch I was shooting within 5g r of each other with same size points). Think I'm right in the middle of the correct spine range (3555 I think and I'm shooting 45lb), but they are cut to 29"

Anyway, with a quiver of ten, equal mix of heavier and lighter and truly shooting them at random as I can't see/feel the difference without checking the points, the heavier are consistently hitting higher at 40 yards by several inches, a little wider spread but not significant... Theories?

I know 25gr isn't a huge difference and the heavier should be about 8-10fps slower depending on your calculator. Does the change in FOC cause this? Only reason I can come up with...

Thanks,
 

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If they were broadheads I'd think it might just be because of a different style head not shooting to the same POI. If they are field tips, not sure. The heavier arrow will carry its velocity better, but I'm not sure if it would show up at 40yds.
 

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Bow Bender
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I would guess two things. When you change the tip weight, you change how that shaft dynamically performs. So it may bend ever so slightly differently upon release, leaving the bow at a different angle than the lighter weight, thus impacting the target at a different (higher in this case) spot. Secondly, with the higher weight, you increase FOC which again affects how your arrow dynamically performs and how it flies and behaves.

Those are my theories.
 

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Don't know but its pretty interesting. I would guess that maybe the heavier arrow is less affected by the vane drag then the lighter arrow. I plan to do some testing of this theory as well as testing of trajectory with differently styles of vanes. Will post results at that point. i'm curious because my 3d bow with light fast arrows has more drop from 20 to 50 yards than my slower hunting bow with heavier arrows. Go figure. Makes it painful to misguess a 3d target by 5 yards lol. With my hunting bow id get an 8 with the 3d bow its a 5. Going to compare Blazers with flex fletch FFP187 and dabble with different point weights at different distances and plot all the results.
 

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Interesting. When something seems to violate the laws of physics, something else is going on. Don't think it's drag as it would be the difference in force for a starting velocity of about 8 fps less - not that much. If your running about 280fps, that's less than 3%. Don't think it's spine as I have seen differences in spine cause left and right changes in POI. Ran a few simulations in OT2 and your 125 gr tipped arrow should have it about 2 1/2" lower and OT2 takes drag into account.
 

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I just had a similar occurrence shooting at 40 yards. One of my arrows is about 3/4 inch shorter than the others (cut off the broken part and refletched it after a collision.) I was sighting in my pin at 40 and the short arrow was consistently impacting about 6" lower than the rest.

I chalked it up to either momentum (slightly heavier arrow takes slightly longer to start dropping.)
 

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Have you shot through the paper?
My guess is the heavier points, especially at 29", is nock low through the paper, hence the difference in poi.
 

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Goldtip chart.jpg Not sure what would cause that if same diameter arrow. It could be spine. Here's the latest GT chart. I think they changed it, not sure, in any case 35-55 is misleading because their 500 spine and your underspined
 

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I'm with Super 91 on this.
However you term the name for it I think this is what is happening.
 

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I know when I shoot my 330 spine arrow 480 grains it hits higher then my 400 spine that's 50 grains lighter. And it's due to a week spine on the 400 spines
 

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View attachment 2349442 Not sure what would cause that if same diameter arrow. It could be spine. Here's the latest GT chart. I think they changed it, not sure, in any case 35-55 is misleading because their 500 spine and your underspined
Way underspined
 

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have bow-will travel
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Fact not theory, the heavier/slower arrows have more of a rainbow trajectory and will always hit to higher POI than lighter/faster arrows at the same distance. Same applies to guns and bullets.
 

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Fact not theory, the heavier/slower arrows have more of a rainbow trajectory and will always hit to higher POI than lighter/faster arrows at the same distance. Same applies to guns and bullets.
You need to brush up on your physics. Heavier will have a more pronounced arc to hit same place,same distance AFTER the sight or scope is changed, untill sight the poi will be lower. In this case it is a spine problem.
 

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Just a stupid question. What rest are you using?
 

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If the only difference is 100 v. 125 tips, then the only factors changed are FOC and flex. The heavies will have smaller FOC but increased flex coming off the rest. The higher POI should be from the reduced FOC.
 

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have bow-will travel
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You need to brush up on your physics. Heavier will have a more pronounced arc to hit same place,same distance AFTER the sight or scope is changed, untill sight the poi will be lower. In this case it is a spine problem.

Don't think so as he is using a sight. I do agree fired at 90* angle to the earth the heavier arrow would always be lower but in this case he is sighted for the lighter arrows which is why the slower arrows are hitting high. Try it yourself and see.
 

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I shot some 503 grain shafts and sighted my bow with these. Then I changed to 527 grain shafts with a much stiffer spine (330's were the 503 shaft, and 250 spine on the 527's), and they all impacted higher out to 50 yards. I did not shoot any further.
 

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Discussion Starter · #19 ·
I'll try to catch all the responses in one...

First, I got the same results shooting with the bow turned down to 42lbs, so is underspine still a consideration? I assumed cutting them down would have stiffened the spine, and I thought a spine issue was usually a left/right issue. The "500" spine has been recommended by everyone from the two local shops to Southshore Archery... Not saying the underspine theory is wrong by any means, but my spine knowledge is lacking except for what I've read (i.e. no real world experience to go on), just the recommendations.

I don't paper tune, or shoot through paper, I can't feel the results without effecting the tear results; just not a technique that is blind friendly. Besides, and this is just my own uneducated take on paper tuning... I've had described to me an arrow's flight after launch (an Easton video I think), and while I know many people see real benefits in paper tuning, I just can't see how with the shaft's flexing during flight nearly all the way to the target how a "bullet hole" tells you anything. I would think moving the paper forward/backwards a few feet/yards would catch the arrow hitting the paper at a different point of the oscillation and give different results...

Not broadheads, field points.

All shafts are the same brand, model, and cut length, I just grabbed some random shafts and swapped out the points... all shot at random without knowing which point I was shooting when; truly a "double blind" study.

I would consider the arc or rainbow theory except because of the design of my tactile aiming stand I know my bow hand elevation, anchor point, and therefore the angle of the bow/arrow during the shot is consistent, so I'm not "introducing" an arc for the heavier shafts. My lefts/rights are consistently inconsistent, my verticals are usually pancake flat when I'm in my "zone."

The rest is a Ripcord Ace.

I thought a higher FOC would cause better vane correction and therefore "better" flight characteristics, but would also drop faster than a lower FOC, but I understand this is at longer yardage and I don't know if shooting such a low DW causes this phenomena at shorter distances or not.

Shooting such a low poundage, could it be merely momentum? Lighter arrow has lost significant velocity faster even at the short distance?

I also know the "throw a ping pong ball and a baseball" analogy, but 25grain difference?

Thanks for all the replies.
 
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